Fuel cell vehicle and water discharging method for fuel cell vehicle

ABSTRACT

A fuel cell vehicle is provided with a fuel cell which generates electric power by a reaction of a reaction gas and discharges water, a tank which accumulates water discharged from the fuel cell, a heater which vaporizes water accumulated in the tank, a discharge valve which switches between accumulating and discharging of the water with respect to the tank, an external air temperature sensor which detects an external air temperature, a vehicle speed sensor which detects a vehicle speed, a selector with which the driver selects an operation of the discharge valve between accumulating and discharging of the water with respect to the tank, and an ECU which controls these components and includes a control section and a control data storage section.

The present invention claims foreign priority to Japanese patent application No. 2005-128503, filed on Apr. 26, 2005, the contents of which is incorporated herein by reference.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a fuel cell vehicle and a water discharging method for a fuel cell vehicle.

2. Description of the Related Art

In recent years, fuel cell vehicles are under vigorous development. Such fuel cell vehicles are equipped with a fuel cell and driven by rotating a drive motor (an electric motor) using an electric power supplied from the fuel cell.

When the fuel cell generates an electric power, water continues to be produced at a cathode (an air electrode) by virtue of an electrode reaction at the cathode. In addition, in order to secure the diffusibility of hydrogen ions (protons) in a solid polymer electrolyte membrane (hereinafter, referred to as an electrolyte membrane) which is part of the fuel cell, there is adopted a method in which for example, humidified air (oxidant gas) is supplied to the cathode side so as to maintain the electrolyte membrane in a wet state. Consequently, water produced at the cathode and contained in humidified air is discharged from the cathode side of the fuel cell, whereas water that has passed through the electrolyte membrane to an anode is discharged from the anode side of the fuel cell (for example, see Japanese Unexamined Patent Publication JP-A-8-321316, paragraph 0016 to 0024 and FIG. 1).

However, such fuel cell vehicles equipped with a fuel cell are driven on public roads, and therefore, there is a demand that water discharged from the fuel cell be not discharged to the outside of the vehicle in the form of liquid.

SUMMARY OF THE INVENTION

It is an object of the present invention to provide a fuel cell vehicle and a water discharging method for a fuel cell vehicle which can discharge water from a fuel cell to the outside of the fuel cell vehicle in a preferable manner.

However, the present invention need not achieve the above objects, and other objects not described herein may also be achieved. Further, the invention may achieve no disclosed objects without affecting the scope of the invention.

According to a first aspect of the present invention, it is preferable that the fuel cell vehicle include a fuel cell which generates electricity by a reaction of a reaction gas and discharges resulting water, an accumulating unit which accumulates the water discharged from the fuel cell, and a vaporizer which vaporizes the water accumulated in the accumulating unit, wherein the water vaporized by the vaporizer is discharged to an outside of the fuel cell vehicle.

As used herein, “vaporization” shall mean not only conversion of liquid into vapor or gas by the application of heat but also atomizing of liquid (hereinafter, referred to as atomization) using an appropriate atomizing device (such as an ultrasonic vibrator and a spraying nozzle which atomizes liquid).

According to the first aspect of the present invention, in the fuel cell vehicle, water discharged from the fuel cell is accumulated in the accumulating unit. Further, the water accumulated in the accumulating unit is heated and vaporized by the vaporizer to be water vapor, and then the water vapor is discharged to the outside of the fuel cell vehicle. Therefore, the discharge of water from the fuel cell vehicle in the form of liquid can be prevented. Consequently, for example, a road surface, such as a surface of a road on which the vehicle is running or parked, is prevented from being water-soaked.

Moreover, also in the case where the water accumulated in the accumulating unit is atomized by the atomizing device, the water is prevented from being discharged from the fuel cell vehicle to a single location in the form of liquid.

According to a second aspect of the present invention, as set forth in the first aspect of the present invention, it is preferable that the fuel cell vehicle further include a switching unit which switches the water to accumulate or to discharge with respect to the accumulating unit, and a control section which controls at least either of the vaporizer or the switching unit.

Therefore, the accumulating and discharging of the water with respect to the accumulating unit can be switched over by the switching unit.

According to a third aspect of the present invention, as set forth in the second aspect of the present invention, it is preferable that the fuel cell vehicle further include an external air temperature sensor which detects an external air temperature, wherein the control section controls at least either of the vaporizer or the switching unit based on the external air temperature detected by the external air temperature sensor.

Therefore, the control section can control at least either of the vaporizer or the switching unit based on the external air temperature detected by the vehicle speed sensor. Furthermore, for example, a configuration may be adopted in which the fuel cell vehicle includes a control data storage section where a predetermined external air temperature data is stored for a comparison with an actual external air temperature (an actually measured external air temperature) detected by the external air temperature sensor. Based on such comparison, in the event that the actually measured external air temperature is lower than the predetermined external air temperature, the control section activates the vaporizer to vaporize accumulated water for subsequent discharge, whereas in the event that the actually measured external air temperature is equal to or higher than the predetermined external air temperature, the control section does not activate the vaporizer but controls the switching unit so that accumulated water is discharged to the outside in the form of liquid. Accordingly, the operation of the vaporizer can be suppressed.

According to a fourth aspect of the present invention, as set forth in the second aspect of the present invention, it is preferable that the fuel cell vehicle further include a vehicle speed sensor which detects a vehicle speed of the fuel cell vehicle, wherein the control section controls at least either of the vaporizer or the switching unit based on the vehicle speed detected by the vehicle speed sensor.

Therefore, the control section can control at least either of the vaporizer or the switching unit based on the vehicle speed detected by the vehicle speed sensor. Furthermore, for example, a configuration may be adopted in which the fuel cell vehicle includes a control data storage section where a predetermined vehicle speed data is stored for comparison with an actual vehicle speed (an actually measured vehicle speed) detected by the vehicle speed sensor with the predetermined vehicle speed. Based on such comparison, in the event that the actually measured vehicle speed is lower than the predetermined vehicle speed, the control section activates the vaporizer to vaporize accumulated water for subsequent discharge, whereas in the event that the actually measured vehicle speed equal to or higher than the predetermined vehicle speed, the control section does not activate the vaporizer but controls the switching unit so that accumulated water is discharged to the outside in the form of liquid. Accordingly, the operation of the vaporizer can be suppressed.

According to a fifth aspect of the present invention, as set forth in the second aspect of the present invention, it is preferable that the fuel cell further include a selector with which a driver selects an operation of the switching unit between accumulating the water and discharging the water, wherein a signal corresponding to accumulate the water or discharge the water is sent to the control section, and the control section controls the switching unit based on the signal sent from the selector.

Therefore, for example, when the fuel cell vehicle is parked at a place where water accumulated in the accumulating unit is allowed to discharge in the form of liquid, a driver can operate the selector to control the switching unit so that the accumulated water can be discharged in the form of liquid.

According to a sixth aspect of the present invention, as set forth in the second aspect of the present invention, it is preferable that the fuel cell further include a liquid level sensor which detects the liquid level of the water accumulated in the accumulating unit, wherein the control section controls at least either of the vaporizer or the switching unit based on the liquid level detected by the liquid level sensor.

According to a seventh aspect of the present invention, as set forth in the first aspect of the present invention, it is preferable that the fuel cell further include an accumulating status indicator which indicates a status of the water accumulated in the accumulating unit.

According to an eighth aspect of the present invention, as set forth in the first aspect of the present invention, it is preferable that the vaporizing unit include a heater which heats the water accumulated in the accumulating unit.

According to a ninth aspect of the present invention, as set forth in the first aspect of the present invention, it is preferable that the vaporizing unit include a atomizer which atomizes the water accumulated in the accumulating unit.

According to a tenth aspect of the present invention, it is preferable that a water discharging method for a fuel cell vehicle include steps of providing accumulating means for accumulating water, accumulating water discharged from a fuel cell in the accumulating means, and vaporizing the water accumulated in the accumulating means, wherein the water vaporized in the vaporizing step is further discharged to an outside of the fuel cell vehicle.

Therefore, the water accumulated in the accumulating unit is heated and vaporized by the vaporizer to be water vapor, and then the water vapor is discharged to the outside of the fuel cell vehicle. Thus, the discharge of water from the fuel cell vehicle in the form of liquid can be prevented. Consequently, for example, a road surface, such as a surface of a road on which the vehicle is running or parked, is prevented from being water-soaked. Moreover, when the water accumulated in the accumulating unit is atomized by an appropriate atomizing device, the water is also prevented from being discharged from the fuel cell vehicle to a single location in the form of liquid.

According to an eleventh aspect of the present invention, as set forth in the tenth aspect of the present invention, it is preferable that the water discharging method for a fuel cell vehicle include steps of discharging the water accumulated in the means to the outside of the fuel cell vehicle, and switching the accumulating step and the discharging step alternatively.

According to a twelfth aspect of the present invention, as set forth in the eleventh aspect of the present invention, it is preferable that the water discharging method for a fuel cell vehicle include step of detecting an external air temperature, wherein at least either of the vaporizing step or the switching step is carried out based on the external air temperature detected in the detecting step.

According to a thirteenth aspect of the present invention, as set forth in the eleventh aspect of the present invention, it is preferable that the water discharging method for a fuel cell vehicle include step of detecting a vehicle speed of the fuel cell vehicle, wherein at least either of the vaporizing step or the switching step is carried out based on the vehicle speed detected in the detecting step.

According to a fourteenth aspect of the present invention, as set forth in the eleventh aspect of the present invention, it is preferable that the water discharging method for a fuel cell vehicle include step of detecting a signal corresponding to accumulate the water or discharge the water with respect to the accumulating means, the signal being selected by a driver, wherein the switching step is carried out based on the signal detected in the detecting step.

According to a fifteenth aspect of the present invention, as set forth in the eleventh aspect of the present invention, it is preferable that the water discharging method for a fuel cell vehicle include step of detecting a liquid level of the water accumulated in the accumulating means, wherein at least either of the vaporizing step or the switching step is carried out based on liquid level detected in the detecting step.

According to a sixteenth aspect of the present invention, as set forth in the tenth aspect of the present invention, it is preferable that the water discharging method for a fuel cell vehicle include step of indicating a status of the water accumulated in the accumulating means.

According to a seventeenth aspect of the present invention, as set forth in the tenth aspect of the present invention, it is preferable that the vaporizing step include step of heating the water accumulated in the accumulating means.

According to an eighteenth aspect of the present invention, as set forth in the tenth aspect of the present invention, it is preferable that the vaporizing step include step of atomizing the water accumulated in the accumulating means.

According to the present invention described above, there can be provided a fuel cell vehicle and a water discharging method for the fuel cell vehicle which can discharge water from the fuel cell to the outside of the fuel cell vehicle in a preferred manner.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a diagram which shows the configuration of a fuel cell vehicle according to an embodiment of the invention; and

FIG. 2 is a flowchart set for the fuel cell vehicle according to the embodiment of the invention.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

Referring to FIGS. 1 and 2, an embodiment of the invention will be described below.

As shown in FIG. 1, a fuel cell vehicle 1 according to the embodiment of the invention is a vehicle having a fuel cell 10 installed thereon. The vehicle is driven by a drive motor which is rotated by an electric power generated in the fuel cell 10. The fuel cell vehicle 1 is provided with the fuel cell 10, an anode system 20 which supplies/discharges a hydrogen gas (a fuel gas, a reaction gas) to/from an anode 12 of the fuel cell 10, a cathode system 30 which supplies/discharges a humidified air (an oxidant gas, a reaction gas) to/from a cathode 13 of the fuel cell 10, an accumulating unit 40 which accumulates water discharged from the fuel cell 10, a vaporizer 50 which vaporizes water accumulated in the accumulating unit 40, a discharge valve 61 (a switching unit) which switches between accumulating and discharging the water with respect to the accumulating unit 40, and an ECU 70 (an Electronic Control Unit). The ECU controls the accumulating unit 40, the vaporizer 50 and the discharge valve 61.

The fuel cell 10 (a fuel cell stack) is constituted by stacking a plurality of unit cells, each having an anode 12 (a fuel electrode), a cathode 13 (an air electrode), a monovalent cation exchange type of electrolyte membrane 11 interposed between the anode and the cathode so as to form a membrane electrode assembly (MEA, a membrane electrode composite unit), and separators sandwiching the MEA therebetween. Grooves for supplying hydrogen gas and humidified air to the overall areas of the respective sides of the electrolyte membrane 11 and through holes for supplying hydrogen gas and humidified air to each of the unit cells are intricately formed on the separators. When hydrogen gas is supplied to the anode 12 as well as humidified air to the cathode 13, a potential difference is produced at the MEA, and the fuel cell 10 is designed to generate electric power to meet a demand for electric power from an outside load such as the drive motor connected to an output terminal of the fuel cell 10.

The anode system 20 is a system which supplies/discharges a hydrogen gas to/from the anode 12 of the fuel cell 10. Hereinafter, a hydrogen gas supply side and a hydrogen gas discharge side of the anode system 20 will be described in that order.

A hydrogen supply side of the anode system 20 includes, as viewed towards a downstream side (towards the fuel cell 10 side), a hydrogen tank 21 where hydrogen gas is stored and an ejector 22. The hydrogen tank 21 is connected to the ejector 22 via a piping 21 a, and the ejector 22 is connected to the anode 12 of the fuel cell 10 via a piping 22 a. A shut-off valve and a pressure reducing valve (both are not shown) are provided along the piping 21 a in that order towards the downstream side. When the shut-off valve is opened, hydrogen gas is adapted to be supplied from the hydrogen tank 21 to the anode 12 of the fuel cell 10 after the pressure thereof has been reduced to a predetermined pressure by the pressure reducing valve.

A hydrogen discharge side of the anode system 20 includes a gas-liquid separator 23, a hydrogen purge valve 24, and a diluter 25 which dilutes unreacted hydrogen gas.

The gas-liquid separator 23 (a catch tank) is equipped to remove water in gas discharged from the anode 12 of the fuel cell 10 (hereinafter referred to as an anode-off gas). The gas-liquid separator 23 is connected to a downstream side of the anode 12 of the fuel cell 10 via a piping 23 a.

In addition, the gas-liquid separator 23 includes a coolant piping (not shown) which carries a coolant so as to cool anode-off gas introduced thereinto to a predetermined temperature to divide the gas into unreacted hydrogen gas and water. However, the gas-liquid separation method of the gas-liquid separator 23 is not limited thereto and a method may be adopted in which the required separation is implemented by a centrifugal force.

A downstream side of the gas-liquid separator 23 is connected to the ejector 22 via a piping 23 b and the diluter 25 via a piping 23 c, respectively. The piping 23 b returns unreacted hydrogen gas to the ejector 22 and is provided at an appropriate location (on an upper wall) of the gas-liquid separator 23 for circulating hydrogen gas. The piping 23 c is provided at an appropriate location (at a bottom wall) of the gas-liquid separator 23 for discharge of separated water (liquid). An open-close valve 26 is provided at a position along the length of the piping 23 c, so that by opening and closing the open-close valve 26 appropriately, water staying in the gas-liquid separator 23 is sent to the diluter 25 as a drain water.

The hydrogen purge valve 24 is an open-close valve and an upstream side thereof is connected to a midway position along the length of the piping 23 c via a piping 24 a. A downstream side of the hydrogen purge valve 24 is connected to the diluter 25 via a piping 24 b. The hydrogen purge valve 24 is opened when the amount of water in circulating hydrogen gas is increased (when hydrogen is purged) or the like.

The diluter 25 (a dilution box) is a equipment having a diluting space in an interior thereof and is adapted to dilute anode-off gas containing unreacted hydrogen gas which is supplied from the piping 24 b. An upstream side of the diluter 25 is connected to the piping 23 c and a piping 31 b, in addition to the piping 24 b.

A piping 25 a which leads diluted hydrogen gas to the outside of the fuel cell vehicle 1 is provided at an appropriate location downstream of the diluter 25. In addition, a piping 25 b is provided at an appropriate location downstream of the diluter 25 which leads drain water separated by the gas-liquid separator 23 to be introduced into the diluter 25 to a tank 41, which will be described later on.

Namely, in the fuel cell vehicle 1 according to the embodiment of the invention, the water discharged from the fuel cell 10, that is, water produced at the cathode 13 as a result of generation of electric power, water which has passed through the electrolyte membrane 11 to the anode 12 and water separated by the gas-liquid separator 23 join together at the diluter 25 so as to be sent to the tank 41 via the piping 25 b.

The cathode system 30 is a system which supplies/discharges humidified to/from the cathode 13 of the fuel cell 10 and includes a compressor 31 (a pump).

To describe an air supply side of the cathode system 30, the compressor 31 is a equipment which takes in external air, compresses the external air so taken in and sends the compressed air to the cathode 13. The compressor 31 is connected to the cathode 13 of the fuel cell 10 via a piping 31 a. In addition, a humidifier (not shown) is provided on the piping 31 a so as to humidify air at the time of normal electric power generation by the fuel cell 10.

To describe an air discharge side of the cathode system 30, the cathode 13 of the fuel cell 10 is connected to the diluter 25 via a piping 31 b, whereby cathode-off gas (humidified air and water produced by virtue of electric power generation at the time of normal electric power generation by the fuel cell 10) discharged from the cathode 13 is designed to be supplied to the diluter 25 via the piping 31 b.

In addition, a back-pressure valve (not shown) is provided on the piping 31 b, so that the pressure of hydrogen gas on the anode side 12 of the fuel cell 10 is balanced with the pressure of air on the cathode side 13 by regulating the back pressure in the piping 31 b. Accordingly, the life of the electrolyte membrane 11 can be extended.

The accumulating unit 40 has a tank 41 and a liquid level sensor 42 (a liquid level detecting device), and accumulates the water discharged from the fuel cell 10.

The tank 41 is disposed at a downstream end of the fuel cell 10, and drain water from the diluter 25 is designed to be supplied into an interior of the tank 41. Drain water from the diluter 25 includes water produced at the cathode 13 by virtue of electric power generation at the fuel cell 10 and water which passes through the electrolyte membrane 11 to the anode 12 side.

An exhaust or gas discharge port 41 a is formed in an upper portion of a side wall of the tank 41. In addition, water vapor vaporized by a heater 51 of the vaporizer 50, which will be described later on, is designed to be discharged to the outside of the fuel cell vehicle 1 by passing through the gas discharge port 41 a and a piping 41 b provided downstream of the gas discharge port 41 a.

In addition, a piping 41 c, which is adapted to discharge water accumulated in the tank 41 in the form of liquid, is provided at a lower portion of the side wall of the tank 41. Additionally, a downstream end of the piping 41 c is connected to the discharge valve 61.

The liquid level sensor 42 is a sensor which detects an actual liquid level (hereinafter, referred to as an actually measured liquid level L11) of water accumulated in the tank 41. As the liquid level sensor 42, a sensor can be used which emits a laser beam to the liquid surface of accumulated water so as to detect a reflected laser beam from the liquid surface.

In addition, the liquid level sensor 42 is electrically connected to a control section 71, which will be described later on, and the control section 71 monitors the actually measured liquid level L11.

The vaporizer 50 has a heater 51, a relay switch 52 and a power supply 53, and vaporizes the water accumulated in the tank 41 by the application of heat thereto. The heater 51 is an electric heater and is disposed in the vicinity of the tank 41 so as to heat and vaporize water within the tank 41. The heater 51 is connected to the power supply 53 via the relay switch 52, and when the relay switch 52 is switched ON, the power supply 53 energizes the heater 51 so that the heater 51 is heated to build up heat. The relay switch 52 is electrically connected to the control section 71, and the control section 71 is adapted to switch ON/OFF the relay switch 52 desirably or to switch ON/OFF the heater 51 desirably. In addition, as the power supply 53, electric power from a battery (a secondary battery) installed on the fuel cell vehicle 1, electric power generated by the drive motor when in a regenerative mode or electric power generated by the fuel cell 10 can be used.

The discharge valve 61 is, for example, an electromagnetic type of open-close valve and is kind of a switching unit which switches between accumulating and discharging of the water with respect to the tank 41. The discharge valve 61 is connected to a downstream end of the piping 41 c. In addition, water is designed to be accumulated in the tank 41 when the discharge valve 61 is closed. On the contrary, when the discharge valve 61 is opened, water within the tank 41 is discharged to the outside of the fuel cell vehicle 1 via a piping 61 a which is connected to a downstream side of the discharge valve 61. In addition, the discharge valve 61 is electrically connected to the control section 71, and the control section 71 is designed to open/close the discharge valve 61 desirably. Furthermore, a diffuser nozzle portion may be provided at a downstream end of the piping 61 a which takes in running air produced by virtue of the running of the fuel cell vehicle 1 so as to diffuse water that is discharged when the discharge valve 61 is opened in such a manner as to be entrained by the running air so taken in.

The ECU 70 includes the control section 71 and a control data storage section 72, provided with such as CPU, ROM, RAM, various types of interfaces, electronic circuits and various types storage media.

The control section 71 is electrically connected to the relay switch 52 and the discharge valve 61 so as to control them desirably. In addition, the control section 71 is electrically connected to the liquid level sensor 42 so as to monitor the actually measured liquid level L11. Furthermore, the control section 71 is electrically connected to an external air temperature sensor 81, which will be described later on, so as to monitor an actual external air temperature (hereinafter, referred to as an actually measured external air temperature T11) which is detected by the external air temperature sensor 81. Moreover, the control section 71 is electrically connected to a vehicle speed sensor 82 so as to monitor an actual vehicle speed (hereinafter, referred to as an actually measured vehicle speed S11) of the fuel cell vehicle 1. In addition, the control section 71 is electrically connected to a selector 83 which is operated by the driver so as to monitor a mode (a discharge mode, an automatic mode, a accumulate mode) selected by the driver. Furthermore, the control section 71 is electrically connected to a accumulating status indicator 84 (a accumulated amount indicator) so as to indicate a accumulated amount in percentage, which will be described later on. Moreover, the control section 71 is connected to an ignition switch (IGSW) of the fuel cell vehicle so as to be interlocked with ON/OFF of the IGSW.

The control section 71 has an external air temperature determination function in which an actually measured external air temperature T11 inputted from the external air temperature sensor 81 is compared with a predetermined external air temperature T1 stored in the control data storage section 72 so as to determine whether or not the actually measured external air temperature T11 is such that water within the tank 41 is allowed to be discharged in the form of liquid (refer to S105 in FIG. 2).

The control section 71 has a vehicle speed determination function in which an actually measured vehicle speed S11 inputted from the vehicle speed sensor 82 is compared with a predetermined vehicle speed S1 stored in the control data storage section 72 so as to determine whether or not the actually measured vehicle speed S11 is such that water within the tank 41 is allowed to be discharged in the form of liquid (refer to step S107 in FIG. 2).

The control section 71 has a mode determination function to determine which of a discharge mode where water in the tank 41 is discharged, an automatic mode where accumulating and discharging of the water with respect to the tank 41 is automatically switched over and a accumulate mode where water is accumulated in the tank 41 corresponds to a mode selected by the driver (refer to S103, S112, S115 in FIG. 2). To be specific, the control section 71 is adapted to determine which of the three modes corresponds to the mode selected by the driver based on a signal sent from the selector 83 which corresponds to the mode selected by the driver. In addition, following a determination so made, the control section 71 is adapted to switch ON/OFF the heater 51 and open/close the discharge valve 61.

The control section 71 has a primary liquid level determination function in which an actually measured liquid level L11 by the liquid level sensor 42 is compared with a primary predetermined liquid level L1 stored in the control data storage section 72 so as to determine whether or not water can be accumulated in the tank 41 (refer to S108, S115 in FIG. 2).

In addition, the control section 71 has a secondary liquid level determination function in which the actually measured liquid level L11 is compared with a secondary predetermined liquid level L2 stored in the control data storage section 72 so as to determine whether or not water can continue to be accumulated as it is without switching ON the heater 51 (refer to S110 in FIG. 2).

The control section 71 has a accumulated amount calculation function to calculate a accumulated amount of water within the tank 41, in percentage, from an actually measured liquid level L11 detected by the liquid level sensor 42 and accumulated amount calculation data stored in the control data storage section 72. In addition, the control section 71 controls the accumulating status indicator 84 to indicate the accumulated amount so calculated in percentage.

The predetermined external air temperature T1, the predetermined vehicle speed S1, the primary predetermined liquid level L1, the secondary predetermined liquid level L2 and the accumulated amount calculation data, each obtained through preliminary experiments and the like, are stored in the control data storage section 72. The control data storage section 72 is electrically connected to the control section 71, and the control section 71 is allowed to refer to the predetermined external air temperature T1 appropriately.

The predetermined external air temperature T1 is an external air temperature which constitutes a reference for determination whether or not water within the tank 41 can be discharged in the form of liquid in the event that the driver selects the automatic mode in which accumulating and discharging of the water with respect to the tank 41 is automatically switched over, and is set to 2 to 10° C., for example. Namely, in the event that the actually measured outside temperature T11 is higher than the predetermined external air temperature T1, the predetermined external air temperature T1 is set to a temperature at which even in case the water within the tank 41 is discharged in the form of liquid to the outside of the fuel cell vehicle 1 on to a road surface, the road surface is not frozen.

The predetermined vehicle speed S1 is a vehicle speed which constitutes a reference for determination whether or not water within the tank 41 can be discharged in the form of liquid in the event that the driver selects the automatic mode, and is set to 20 km/h, for example. Namely, in the event that the actually measured vehicle speed S11 is higher than the predetermined vehicle speed S1, the predetermined vehicle speed S1 is set to a vehicle speed at which even in case the water within the tank 41 is discharged in the form of liquid to the outside of the fuel cell vehicle 1, the discharged water is prevented from being spread into the external air by running air produced by the running vehicle to thereby wet the surface of a road.

The primary predetermined liquid level L1 is a liquid level which constitutes a reference for determination whether or not additional water can be accumulated within the tank 41. Namely, the primary predetermined liquid level L1 is a liquid level which constitutes a reference for determination whether or not the tank 41 is full of water. Thus, the overflow of water from the tank 41 is designed to be prevented by setting the primary predetermined liquid level L1 for comparison with the actually measured liquid level L11.

The secondary predetermined liquid level L2 is a liquid level which constitutes a reference for determination whether or not additional water can be accumulated within the tank 41 without switching ON the heater 51 in the event that the driver selects the automatic mode. Namely, in the event that an extra space for storage of water still remains in the tank 41 and the primary predetermined liquid level L1 is higher than the actually measured liquid level L11 whereas the actually measured liquid level L11 is higher than the secondary predetermined liquid level L2, the secondary predetermined liquid level L2 is set to a liquid level at which even in case additional water is accumulated within the tank 41 without switching ON the heater 51, the overflow of water does not take place immediately thereafter.

The accumulated amount calculation data are data which relate the level of liquid within the, tank 41 to the accumulated amount in percentage (a so-called calibration curve).

In addition, the fuel cell vehicle 1 includes the external air temperature sensor 81, the vehicle speed sensor 82, the selector 83 and the accumulating status indicator 84.

The external air temperature sensor 81 is a temperature sensor which detects an actually measured external air temperature T11 of the fuel cell vehicle 1 and is mounted on an appropriate location (a body) of the fuel cell vehicle 1.

The vehicle speed sensor 82 is a sensor which detects an actually measured vehicle speed S11 of the fuel cell vehicle 1 and is mounted on an appropriate location of the fuel cell vehicle 1.

The selector 83 with which the driver selects a mode from the discharge mode, automatic mode and accumulate mode based on his or her own will is provided on the periphery of the driver's seat. The selector 83 has a selecting lever 83 a with which positions corresponding to the discharge mode, automatic mode and accumulate mode can be selected, so that the driver can select a mode from the discharge mode, automatic mode and accumulate mode by controlling the selecting lever 83 a.

The accumulating status indicator 84 is a monitor which indicates a accumulated amount of water within the tank 41 in percentage and is disposed on the instrument panel or the like, whereby the driver can visually recognize the accumulated amount of water.

Next, referring to FIG. 2, in addition to FIG. 1, a water discharging method for the fuel cell vehicle 1 will be described along with a flowchart set for the control section 71. A water discharging method for the fuel cell vehicle 1 includes the step of heating and vaporizing water discharged from the fuel cell 10 and accumulated in the tank 41 for discharge to the outside of the fuel cell vehicle 1. Note that the control section 71 executes repeatedly a process in each step of the flowchart shown in FIG. 2.

Firstly, a normal electric power generation by the fuel cell 10 will be described simply.

When hydrogen gas (reaction gas) is supplied to the anode 12 and humidified air containing oxygen (reaction gas) is supplied to the cathode 13, an electrode reaction takes place at either of the anode 12 and the cathode 13, whereby a potential difference occurs in the MEA which makes up the fuel cell 10. When a demand for electric power rises from an external load such as the drive motor in such a state that the potential difference is occurring, the fuel cell 10 generates electric power.

Water continues to be produced at the cathode 13 due to the electric power generation occurring thereat. Water (water vapor) so produced is sent to the diluter 25 together with water in the humidified air supplied to the cathode 13 as cathode-off gas. On the other hand, part of water contained in humidified air that is supplied to the cathode 13 and part of water produced at the cathode 13 passes through the electrolyte membrane 11 to reach the anode 12 and is then sent to the gas-liquid separator 23 while being contained in anode-off gas. Following this, gas and liquid are separated from each other at the gas-liquid separator 23, and water so separated thereat (water that has passed through the electrolyte membrane 11 and the like) is sent to the diluter 25. Then, water sent from the cathode 13 of the fuel cell 10 and water separated at the gas-liquid separator 23 is sent from the diluter 25 to the tank 41 as drain water.

Next, processing conducted by the control section 71 will be described which takes place in such a situation that water discharged from the fuel cell 10 as described above by virtue of the normal electric power generation by the fuel cell 10 is sent to the tank 41.

In step S101, the control section 71 detects an actually measured liquid level via the liquid level sensor 42.

In step S102, the control section 71 calculates an actual accumulated amount of water, in percentage, from the actually measured liquid level L11 so detected and the accumulated amount calculation data stored in the control data storage section 72. Following this, the control section 71 controls the accumulating status indicator 84 to indicate the accumulated amount so calculated in percentage.

In step S103, the control section 71 determines whether or not the mode selected by the driver is the automatic mode. To be specific, the control section 71 determines whether or not a signal corresponding to the automatic mode position of the selecting lever 83 a is being sent from the selector 83.

If the control section 71 determines that the mode selected by the driver is the automatic mode (S103, Yes), the processing proceeds to a step S104. On the contrary, if the control section 71 determines that the mode selected by the driver is not the automatic mode, the processing proceeds to a step S112.

Note that when proceeding to the step S104, it is when the automatic mode is selected, while when proceeding to the step S112, it is when either the discharge mode or the accumulate mode is selected.

In the step S104, the control section 71 detects an actually measured external air temperature T11 via the external air temperature sensor 81.

Next, in a step S105, the control section 71 compares the actually measured external air temperature T11 so detected with the predetermined external air temperature T1 stored in the control data storage section 72, so as to determine whether or not the actually measured external air temperature T11 is an external air temperature at which the water within the tank 41 is allowed to be discharged in the form of liquid.

In the event that the actually measured external air temperature T11 is lower than the predetermined external air temperature T1, the control section 71 determines that the actually measured external air temperature T11 is an external air temperature at which water within the tank 41 is prohibited from being discharged in the form of liquid (S105, Yes), and the processing proceeds to a step S106. Therefore, even in the event that the external air temperature is low, water within the tank 41 is not discharged in the form of liquid, thereby avoiding a risk of the road surface or the like being frozen due to tank water which would otherwise be discharged.

On the other hand, in the event that the actually measured external air temperature T11 is equal to or higher than the predetermined external air temperature T1, the control section 71 determines that the actually measured external air temperature T11 is an external air temperature at which water within the tank 41 is allowed to be discharged in the form of liquid (S105, No), and the processing proceeds to a step S113. Therefore, the water within the tank 41 can be discharged in the form of liquid in such a situation that there exists no risk of the road surface or the like being frozen.

In the step S106, the control section 71 detects an actually measured vehicle speed S11 via the vehicle speed sensor 82.

In a step S107, the control section 71 compares the actually measured vehicle speed S11 so detected with the predetermined vehicle speed S1 stored in the control data storage section 72, so as to determine whether or not the actually measured vehicle speed S11 is a vehicle speed at which water within the tank 41 is allowed to be discharged in the form of liquid.

In the event that the actually measured vehicle speed S11 is lower than the predetermined vehicle speed S1, the control section 71 determines that the actually measured vehicle speed S11 is a vehicle speed at which water within the tank 41 is prohibited from being discharged in the form of liquid (S107, Yes), and the processing proceeds to a step S108. Therefore, even in the event that the actually measured vehicle speed S11 is slow, water within the tank 41 is not discharged in the form of liquid, and the road surface is prevented from being wetted by tank water which would otherwise be discharged.

On the other hand, in the event that the actually measured vehicle speed S11 is equal to or higher the predetermined vehicle speed S1, the control section 71 determines that the actually measured vehicle speed S11 is a vehicle speed at which water within the tank 41 is allowed to be discharged in the form of liquid (S107, No), and the processing proceeds to the step S113. Therefore, water discharged from the tank 41 in the form of liquid can be prevented from being spread into the external air due to running air produced by the running vehicle to eventually wet the road surface.

In a step S108, the control section 71 compares the actually measured liquid level L11 with the primary predetermined liquid level L1, so as to determine whether or not the actually measured liquid level L11 is a liquid level which allows additional water to be accumulated in the tank 41.

In the event that the actually measured liquid level L11 is lower than the primary predetermined liquid level L1, the control section 71 determines that the actually measured liquid level L11 is a liquid level which allows additional water to be accumulated in the tank 41 (S108, Yes), and the processing proceeds to a step S109.

On the other hand, in the event that the actually measured liquid level L11 is equal to or higher than the primary predetermined liquid level L1, the control section 71 determines that the actually measured liquid level L11 is a liquid level which prohibits additional water from being accumulated in the tank 41 (S108, No), and the processing proceeds to the step S113, whereby the overflow of water from the tank 41 is prevented.

In the step S109, the control section 71 closes the discharge valve 61. In the event that the discharge valve 61 has already been closed, the control section 71 keeps the discharge valve 61 closed. Thereafter, the processing proceeds to a step S110.

In the step S110, the control section 71 compares the actually measured liquid level L11 with the secondary predetermined liquid level L2, so as to determine whether or not the actually measured liquid level L11 is a liquid level which allows additional water to be accumulated in the tank 41 without switching ON the heater 51 (switching On the relay switch 52).

In the event that the actually measured liquid level L11 is higher than the secondary predetermined liquid level L2, the control section 71 determines that an extra space for accumulating additional water remains little within the tank 41, needing to switch ON the heater (S110, Yes), and the processing proceeds to a step S111.

On the other hand, in the event that the actually measured liquid level L11 is equal to or lower than the secondary predetermined liquid level L2, the control section 71 determines that the actually measured liquid level L11 is a liquid level which produces an extra space within the tank 41 for storage of additional water without switching ON the heater 51 (S110, No), and the processing proceeds to RETURN and thereafter returns to START.

Thus, since, in the step S110, the heater 51 is switched ON and OFF (the relay switch 51 is switched ON/OFF) based on the level of water accumulated (the accumulated amount of water) in the tank 41, the consumption of electric power at the power supply 53 by the heater 51 can be reduced.

In the step S111, the control section 71 switches ON the relay switch 52 so as to switch ON the heater 51. Note that in the event that the heater 51 has already been switched ON, the control section 71 keeps the heater 51 switched ON.

Due to the control by the control section 71 like this, the heater 51 generates heat, so as to heat water within the tank 41. Then, water within the tank 41 is vaporized to be converted into water vapor, and water vapor is then discharged to the outside of the fuel cell vehicle 1 via the gas discharge port 41 a and the piping 41 b. Thus, since water within the tank 41 is discharged to the outside in the form of water vapor, the road surface is prevented from being wetted by tank water which would otherwise be discharged in the form of liquid.

Thereafter, the processing proceeds to RETURN and then returns to START.

Next, a case will be described in which the determination made in the step S103 is negative and the processing proceeds to the step S112.

In the step S112, the control section 71 determines whether or not the mode selected by the driver is the discharge mode. To be specific, the control section 71 determines whether or not a signal corresponding to the discharge mode position of the selecting lever 83 a is being sent from the selector 83.

If the control section 71 determines that the mode selected by the driver is the discharge mode (S112, Yes), the processing proceeds to the step S113. On the contrary, if the control section 71 determines the mode selected by the driver is not the discharge mode (S103, No), the processing proceeds to a step S115. Note that when proceeding to the step S115, it is when the driver selects the accumulate mode.

In the step S113, the control section 71 opens the discharge valve 61, whereby water within the tank 41 is discharged. Note that in the event that the discharge valve 61 has already been opened, the control section 71 keeps the discharge valve 61 opened. Then, the processing proceeds to a step S114.

In the step S114, the control section 71 switches OFF the relay switch 52, so as to switch OFF the heater 51. Note that in the event that the heater 51 has already been switched OFF, the control section 71 keeps the heater 51 switched OFF, whereby water that is being discharged is prevented from being heated by the processing carried out in the step S113. Namely, the consumption of electric power at the power supply 53 by the heater 51 can be reduced.

Thereafter, the processing proceeds to RETURN and then returns to START.

In the step S115, the control section 71 compares the actually measured liquid level L11 with the primary predetermined liquid level L1, as did in the step S108, so as to determine whether or not the actually measured liquid level L11 is a liquid level which allows additional water to be accumulated in the tank 41.

In the event that the actually measure liquid level L11 is lower than the primary predetermined liquid level L1, the control section 71 determines that additional water can be accumulated (S115, Yes), and the processing proceeds to a step S116. On the other hand, in the event that the actually measure liquid level L11 is equal to or higher than the primary predetermined liquid level L1″, the control section 71 determines that no more water can be accumulated (S115, No), and the processing proceeds to the step S113, whereby the overflow of water from the tank 41 is prevented.

In the step S116, the control section 71 closes the discharge valve 61. In the event that the discharge valve 61 has already been closed, the control section 71 keeps the discharge valve 61 closed. Thereafter, the processing proceeds to a step S117.

In the step S117, the control section 71 switches OFF the relay switch 52, so as to switch OFF the heater 51, as did in the step S114. Note that in the event that the heater 51 has already been switched OFF, the control section 71 keeps the heater 51 switched OFF, whereby in the event that the driver selects the accumulate mode (S103, No; S112, No) and the tank 41 can accumulate additional water (S115, Yes), the heater 51 is switched OFF, thereby making it possible to reduce the consumption of electric power at the power supply 53 by the heater 51.

Thereafter, the processing proceeds to RETURN and then returns to START.

Thus, while the preferred embodiment of the invention has been described heretofore, the invention is not limited thereto but can be modified appropriately without departing from the spirit and scope thereof.

While, in the aforesaid embodiment, the liquid level detection unit for detecting the actually measured liquid level L11 of water within the tank 41 has the liquid level sensor 42, the invention is not limited thereto, and hence, the liquid level detection unit may have a float.

While, in the aforesaid embodiment, water discharged from the fuel cell 10 and the like is described as joining at the diluter 25 with the tank 41 being positioned downstream of the diluter 25, in addition to this configuration, for example, another configuration may be adopted in which water discharged from the fuel cell 10 is not made to so join, and the tank 41 (the accumulating unit 40), the heater 51 (the vaporizer 50) and the discharge valve 61 (the switching unit) are provided on the downstream side of each of the anode 12 and the cathode 13 of the fuel cell 10.

While, in the aforesaid embodiment, the vaporizer 50 has the heater 51 which generates heat by virtue of electric power, in addition to this configuration, for example, another configuration may be adopted in which the vaporizer 50 may be have an ultrasonic vibrator, in place of the heater 51, so that water within the tank 41 is vibrated by ultrasonic waves generated by the vibrator so as to be atomized (vaporized). Thus, in the event that the vaporizer 50 has the ultrasonic vibrator, since there occurs no state shift of water from liquid to vapor or gas in company with the generation of ultrasonic waves, the consumption of electric power (energy) at the power supply 53 can be reduced.

While there has been described in connection with the preferred embodiments of the present invention, it will be obvious to those skilled in the art that various changes and modification may be made therein without departing from the present invention, and it is aimed, therefore, to cover in the appended claim all such changes and modifications as fall within the true spirit and scope of the present invention. 

1. A fuel cell vehicle comprising: a fuel cell which generates electricity by a reaction of a reaction gas and discharges water; an accumulating unit which accumulates the water discharged from the fuel cell; and a vaporizer which vaporizes the water accumulated in the accumulating unit, wherein the water vaporized by the vaporizer is discharged to an outside of the fuel cell vehicle.
 2. The fuel cell vehicle according to claim 1, further comprising: a switching unit which switches the water to accumulate or to discharge with respect to the accumulating unit; and a control section which controls at least either of the vaporizer or the switching unit.
 3. The fuel cell vehicle according to claim 2, further comprising: an external air temperature sensor which detects an external air temperature, wherein the control section controls at least either of the vaporizer or the switching unit based on the external air temperature detected by the external air temperature sensor.
 4. The fuel cell vehicle according to claim 2, further comprising: a vehicle speed sensor which detects a vehicle speed of the fuel cell vehicle, wherein the control section controls at least either of the vaporizer or the switching unit based on the vehicle speed detected by the vehicle speed sensor.
 5. The fuel cell vehicle according to claim 2, further comprising: a selector with which a driver selects an operation of the switching unit between accumulating the water and discharging the water, wherein a signal corresponding to accumulate the water or discharge the water is sent to the control section, and the control section controls the switching unit based on the signal sent from the selector.
 6. The fuel cell vehicle according to claim 2, wherein the accumulating unit includes: a liquid level sensor which detects the liquid level of the water accumulated in the accumulating unit, wherein the control section controls at least either of the vaporizer or the switching unit based on the liquid level detected by the liquid level sensor.
 7. The fuel cell vehicle according to claim 1, further comprising: an accumulating status indicator which indicates a status of the water accumulated in the accumulating unit.
 8. The fuel cell vehicle according to claim 1, wherein the vaporizing unit includes a heater which heats the water accumulated in the accumulating unit.
 9. The fuel cell vehicle according to claim 1, wherein the vaporizing unit includes a atomizer which atomizes the water accumulated in the accumulating unit.
 10. A water discharging method for a fuel cell vehicle comprising steps of: providing accumulating means for accumulating water; accumulating water discharged from a fuel cell in the accumulating means; and vaporizing the water accumulated in the accumulating means, wherein the water vaporized in the vaporizing step is discharged to an outside of the fuel cell vehicle.
 11. The water discharging method for a fuel cell vehicle according to claim 10, further comprising step of: discharging the water accumulated in the means to the outside of the fuel cell vehicle; and switching the accumulating step and the discharging step alternatively.
 12. The water discharging method for a fuel cell vehicle according to claim 11, further comprising steps of: detecting an external air temperature, wherein at least either of the vaporizing step or the switching step is carried out based on the external air temperature detected in the detecting step.
 13. The water discharging method for a fuel cell vehicle according to claim 11, further comprising step of: detecting a vehicle speed of the fuel cell vehicle, wherein at least either of the vaporizing step or the switching step is carried out based on the vehicle speed detected in the detecting step.
 14. The water discharging method for a fuel cell vehicle according to claim 11, further comprising step of: detecting a signal corresponding to accumulate the water or discharge the water with respect to the accumulating means, the signal being selected by a driver, wherein the switching step is carried out based on the signal detected in the detecting step.
 15. The water discharging method for a fuel cell vehicle according to claim 11, further comprising step of: detecting a liquid level of the water accumulated in the accumulating means, wherein at least either of the vaporizing step or the switching step is carried out based on liquid level detected in the detecting step.
 16. The water discharging method for a fuel cell vehicle according to claim 10, further comprising step of: indicating a status of the water accumulated in the accumulating means.
 17. The water discharging method for a fuel cell vehicle according to claim 10, wherein the vaporizing step includes step of heating the water accumulated in the accumulating means.
 18. The water discharging method for a fuel cell vehicle according to claim 10, wherein the vaporizing step includes step of atomizing the water accumulated in the accumulating means. 